Muscle cramps are a common complication of hemodialysis treatments, occurring in 33 to 86 percent of patients [1-3]; they often result in the early termination of a hemodialysis session and are therefore a significant cause of underdialysis. The exact etiology of cramps in dialysis patients is unknown. Since cramps tend to occur most frequently near the end of hemodialysis treatments, changes in plasma osmolality and/or extracellular fluid volume have been implicated.

A cramp is a prolonged involuntary muscle contraction that occurs in a muscle that voluntarily contracts when it is already in its most shortened position [4]. The increased frequency of cramps at rest and during the night may be caused by the placement (by the plantar-flexed foot) of the calf and ventral foot muscles in the most shortened and vulnerable position during sleep [4].

Electromyography reveals that cramps begin with fasciculations in various muscle parts that subsequently progress to high-frequency action potentials. The origin of a cramp is therefore neural, not muscular [4].

The etiology of hemodialysis-associated cramps may include contributions from one or more of the following factors [1,4,5]:

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